Gonadal steroid hormones regulate reproductive and social behaviors in many vertebrates. In several species it has been demonstrated that steroids effect behavioral changes by acting on the preoptic area of the hypothalamus. However, the mechanism by which hormone stimulation induces behavioral change is unknown. Data on territorial scent marking in the Mongolian gerbil suggests that hormone stimulation may alter RNA and protein synthesis in preoptic area cells and thus elicit the behavior (Thiessan & Yahr, 1970; Thiessen, Yahr & Owen, 1973). The proposed research uses a unique approach to determine if changes in gerbil scent marking do result from changes in preoptic area cellular components, particularly proteins. Hormone dependent changes in marking behavior are examined as well as individual differences in scent marking frequency in response to hormone stimulation. Immunochemical techniques are used to detect changes in gerbil preoptic area cellular components associated with different hormonal states and different levels of scent marking. Antibodies will be developed against preoptic area tissue fractions taken from castrated male gerbils receiving either testosterone replacement therapy (high levels of scent marking) or control injections (low levels of marking). The antibodies will be assayed for their reactions with each tissue fraction by two-dimensional immunodiffusson; this will determine if the tissue fractions contain different cellular components as a result of differential hormone treatment. To determine if component differences are related to variations in territorial marking, the immunochemical assays will be repeated using preoptic area tissue fractions from varous classes of gerbils that differ in marking frequency and/or hormonal state. An attempt will also be made to manipulate scent marking with antibody injections.